1. Field of the Invention
The present invention relates to a display device applied to an image forming apparatus such as a printer, and more particularly, to an arrangement of a source of light for illuminating a liquid-crystal display panel.
2. Description of the Related Art
FIG. 6 is a view explaining a known display device. This known display device includes a liquid-crystal display panel 11 of a rectangular shape, a point-like light source in the form of an LED 15 that is arranged adjacent to an illustrated left side portion of the liquid-crystal display panel 11, a display driver IC 12 that is arranged outside of an illustrated lower side portion of the liquid-crystal display panel 11, and a casing 13 that supports the entire display device.
FIG. 7 is a view showing the state in which the liquid-crystal display panel 11 of FIG. 6 has been removed for explanation of the parts arranged at a rear side of the liquid-crystal display panel 11. Reference numeral 14 designates a light guide plate for guiding the light of the LED 15.
FIG. 8 is a view explaining the distance relationship between a liquid crystal display area 16 of the liquid-crystal display panel 11 and the LED 15. The liquid crystal display area 16 is a smaller-size area within the liquid-crystal display panel 11. Reference character A represents the shortest distance from the LED 15 to the liquid crystal display area 16, and reference character B′ represents the width of the entire apparatus in the illustrated right-and-left or horizontal direction (i.e., longitudinal direction of the liquid crystal display area) of that side of th casing 13 at which the LED 15 is arranged.
Now, reference will be made to a back light unit of the display device as constructed above. The light emitted from the LED 15 enters the light guide plate 14 from its light-receiving surface, and is guided to diffuse by the light guide plate 14. In this case, the diffusing light, which has gone through the light guide plate 14 to the side opposite the liquid-crystal display panel 11, is reflected by the casing 13 to pass through the light guide plate 14 and the liquid-crystal display panel 11. On the other hand, the diffusing light, which has passed to the side of the liquid crystal display panel 11, directly goes through the liquid-crystal display panel 11.
The closer to the liquid crystal display area 16 the LED 15 is disposed, the brighter it acts as a back light for the liquid-crystal display panel 11; however, if the LED 15 is disposed too close to the liquid-crystal display panel 11, the neighborhood of the LED 15, acting as a light source, becomes too bright, thus generating unevenness in luminance.
In view of such a circumstance, the LED 15 is disposed at a side of the liquid-crystal display panel 11 while ensuring the appropriate distance A therebetween so as to suppress the luminance unevenness within an allowable range. However, it is necessary to ensure such a distance A, thus resulting in the problem that reduction in the entire width B′ of the apparatus is difficult.